Re: typedef union

"Nils Wagner" <[email protected]> wrote in message 
news:[email protected]...
> Hi all,
>
> I am newbie to ctypes.
>
> How can I "translate" the following C-code into Python ?
> I don't know how to handle HEAD and memcpy ?
> Any pointer would be appreciated.
>
> Thanks in advance.
>
> Nils
>
>
>       typedef union {
> int i;
> float f;
> char c[4];
> } Word;
>
>       int
> I,J,K,N,IDE,IA,IE,IERR,JUNIT,JUNCAT,NDATA,NREC,LREADY,ONE=1;
>       Word BUF[100],HEAD[30];
>
>       for (I=5;I<LHEAD;I++)
> HEAD[I].i = 0;
>       HEAD[ 0].i = 1;
>       HEAD[ 1].i = LHEAD + NDATA*7;
>       HEAD[ 2].i = LHEAD;
>       HEAD[ 3].i = NDATA;
>       HEAD[ 4].i = 7;
>       memcpy (HEAD[ 7].c,"DSIO",4);
>       memcpy (HEAD[ 8].c,"TEST",4);
>       memcpy (HEAD[ 9].c,"NPCO",4);
>       memcpy (HEAD[10].c," ",4);
>       memcpy (HEAD[11].c,"DSIO",4);
>       HEAD[20].i = 1;
>       HEAD[21].i = NDATA;
>       STRING = "MM RAD";
>       DSEINH(STRING,&HEAD[24].i,&ONE,
> strlen(STRING));

Here's a rough translation.  Note how the arrays are declared.  "c_char*4" 
is a 4-character array *type*.  (Word*100)() is a 100-Word array *instance*. 
To assign to the char array, just use a maximum 4-character string.

import ctypes

class Word(ctypes.Union):
    _fields_ = [
        ('i',ctypes.c_int),
        ('f',ctypes.c_float),
        ('c',ctypes.c_char*4)]

I=J=K=N=IDE=IA=IE=IERR=JUNIT=JUNCAT=NDATA=NREC=LREADY=ONE=1
BUF = (Word*100)()
HEAD = (Word*30)()

# not defined in C code
LHEAD = 30

for I in range(5,LHEAD):
    HEAD[I].i = 0

HEAD[ 0].i = 1;
HEAD[ 1].i = LHEAD + NDATA*7
HEAD[ 2].i = LHEAD
HEAD[ 3].i = NDATA
HEAD[ 4].i = 7
HEAD[ 7].c = "DSIO"
HEAD[ 8].c = "TEST"
HEAD[ 9].c = "NPCO"
HEAD[10].c = " "
HEAD[11].c = "DSIO"
HEAD[20].i = 1
HEAD[21].i = NDATA
STRING = "MM RAD"
# Not enough info
# DSEINH(STRING,&HEAD[24].i,&ONE,strlen(STRING));

-Mark



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